The present invention relates to sizing compositions for glass fibers used to reinforce plastics, sized fibers and plastic articles reinforced with said sized fibers.
Glass fiber reinforced plastics, whether thermoplastic or thermosetting, typically contain impurities which generally cause yellowing. Historically, this discoloration has been counteracted by the addition of a blue pigment or dye to the plastic. As a result of color compensation, the plastic appears whiter, although in fact it is actually grayer because of the loss of lightness due to absorption of light by the pigment or dye. More recently, a better way to counteract the yellow discoloration has been with the aid of fluorescent whitening or brightening agents (FWA) also referred to as optical brighteners. Since the yellow cast is produced by absorption of short wave-length light, with the FWA, the lost light is partially replaced by fluorescence of the brightener, thus producing a complete white without loss of light. The brightener typically absorbs the invisible ultraviolet portion of the daylight spectrum and converts this energy into the longer wavelength visible portion of the spectrum.
Japanese Kokoku 6[1994]-4720 and 5[1993]65537 exemplify glass fiber reinforced thermoplastic polymers in which a fluorescent whitening agent is added with the binder for the glass fiber. U.S. Pat. No. 4,609,591 discloses a 100 percent solids, nonaqueous sizing composition for glass fibers which contains a whitening agent.
Notwithstanding the advantages of FWA, coloration problems still remain. When blending a FWA into a plastic matrix polymer, in order to prevent discoloration satisfactorily, the FWA must disperse well in the matrix polymer. However, at the low levels in which FWA are typically used, uniform blending of the brightener with the matrix polymer can be difficult to achieve and, moreover, physical properties of the plastic are sometimes detrimentally affected.
There is a need, therefore, for a convenient way to achieve glass fiber reinforced plastics with good physical properties, which do not yellow and are easily and economically processed.